Just thought I'd update....
Have changed the oil, oil and air filters, fuel filter etc. The old oil that came out was nasty, not sure if it had been mixed with something (not milky though). Ran it through with some cheap oil for 100 miles then dumped and good 5w30 fully synth put through. The difference it's made to the sound of the engine is unreal, oil can light's gone off now and hasn't come back on. Done 150 miles this morning on motorway and it's been good.
To anyone who's reading this having had similar issues, I'd recommend this be done.
Cheers cheers..